This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Collagen fiber and fibril diameter and orientation in tissue can vary greatly in disease processes such as asthma and chronic obstructive pulmonary disorder, which are characterized by airway collagen deposition and scar formation. Pathological changes in collagen microstructure affect mechanical properties of extracellular matrix, which may affect both cell behavior and gross tissue and organ mechanical properties. By systematically varying the microstructure of collagen hydrogels, basic tissue engineering scaffolds, we can change both hydrogel mechanical properties and linear and nonlinear scattering properties in a controlled manner. The purpose of this study is to correlate changes in collagen hydrogel optical properties (second harmonic generation, SHG, and two-photon fluorescence, TPF) with changes in hydrogel mechanical properties over a range of polymerization conditions.